LED backlight conversion using recycled CCFL inverter parts

[Ammon] repairs busted LCD monitors as a side hobby, so replacing burned out CCFLs and inverter circuits is something he can do in his sleep. One Dell monitor he received had him so perplexed, that he simply gave up on trying to repair the inverter circuit. He still wanted to get it working, so he had some narrow PCBs made and started working on his LED replacement backlight.

He built a driver board for the LEDs, populated with left over components that he stripped from the LCD panel’s inverter circuit. He needed space to insert his driver board, so he simply cut out a chunk of the inverter board and slipped his replacement driver board in its place. As you can see in the picture above, his board (in green) takes up far less space than the original inverter circuit it replaces.

He provides a schematic for his circuit as well as a PCB layout file, so it should be fairly easy to replicate his work. He has not posted schematics or layout information for his LED strips, but we’re betting he will if someone asks nicely.

Check out this pair of posts if you are interested in reading more about replacing your burned out CCFL with LEDs.

I’ve got stacks and stacks of these monitors and the next model in Dell’s lineup – Stuffed in random corners at the office because the dumpster’s too far away to get around to hauling them out there. Patch them up for dollars? Never considered it. Maybe a good time to get some hands-on electronics practice…

@Ben: The E172FPb’s typically fail because of bad solder joints which end up burning out the inverter transistors. The business-line LCDs (1704xxx’s and 1905’s) typically fail due to capacitors blowing. I don’t repair them much any more (too busy with other projects), but I got to the point where I could do a complete repair in 20-30 minutes, and turn the monitors around for a $20 profit.

Yeah, this is a really common and easy to fix problem if you know what you’re looking for.
You check the transistor pairs on the backlight section to find the shorted ones, replace them, reflow the solder joints on the capacitor and related transformers, then replace the fuse and throw it all back together.

@Mohonri I’ve replaced capacitors on these before, works about 75% of the time.

I’ve often wondered if the existing CCFL could be repurposed, by taking two “bad” transformers and rewinding the secondaries with a few turns of 22 gauge.
This would also get around the problem of the monitor shutting down which happens if one inverter is fried.

It should work, on most monitors the CCFL transformers are wired in parallel.

Always thought about doing something like this, but could never figure out a good, evenly lit design – The light strip design here is simply elegant – This guy needs to protect the idea before some manufacturer steals it…

That said, I’ve had my hand in CCFL repairs as well – If you’ve got some spare cash and time, you can make a decent profit on laptops – Buy one with a “dim” or “red” screen, and odds are it’s either the bulb or (less likely) the inverter – The average repair cost for me was ~$15, versus $50-300 for a new screen – Which is why people are willing to dump laptops like that for next to nothing…

Repairing a monitor can be sooo easy…
LG screen didn’t turn on anymore, got bored with the trick of repeatedly pulling/reinserting the power cord and mashing the powerbutton.
Opened it up, and the condensators in the low-voltage stage looked funky (“poped” top), replaced all 5 to be sure and it’s working again.
10 minutes to open the damn thing up, don’t be afraid to pull those plastic latches hard, 2euro for the condensators and 10 minutes of soldering.
that beats the shit out of paying for a new one.